As I understand it, a lead SNP captures the variance for all unmeasured SNPs in a region due to it's low p-value and high linkage disequilibrium. However, in different papers the region size differs (e.g. from 500kb +/- to 1mb +/-), how are these sizes chosen and why do they differ?
Edit to add examples: Xia et al. Transl Psychiatry. 2017 Aug "Genome-wide association analysis identifies common variants influencing infant brain volumes" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5611727/ -500kb region
Polushina et al. Transl Psychiatry. 2017 Dec "Analysis of the joint effect of SNPs to identify independent loci and allelic heterogeneity in schizophrenia GWAS data" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5802566/ -1mb region